1. Field
The following description relates to a Schmitt trigger circuit, and to a logic gate using a Schmitt trigger circuit.
2. Description of Related Art
A Schmitt trigger circuit is a circuit outputting “0” or “1” by controlling a threshold voltage used as a reference voltage in which an output signal is changed according to a change of an input signal, and making different threshold voltages according to the change of the input signal.
The circuit performs an operation of increasing an output voltage when an input voltage is greater than a predetermined value, and of decreasing the output voltage when the output voltage is equal to or smaller than the predetermined value. The Schmitt trigger circuit is a circuit that sensitively operates according to a value of the input voltage, and is a circuit in which a state of the output voltage changes at two different trigger voltages. That is, the Schmitt trigger circuit changes the state of the output voltage at a lower trigger point (LTP) and an upper trigger point (LTP).
Due to the characteristics, the Schmitt trigger circuit has characteristics in which the output is not easily changed and maintains an original value even when noise is applied to a signal transmission path. Thus, the Schmitt trigger circuits is mainly used to improve noise immunity of the circuit.
Schmitt trigger circuits that are conventionally used, there is a path to flow an additional current for maintaining the output during transition of a signal.
For this reason, a conventional Schmitt trigger circuit needs a transistor for flowing the additional current in addition to a circuit constituting a logic gate, and generally, the number of added transistors is greater than the number of transistors used in a conventional logic gate.
In order to reduce an area of a circuit due to a degree of integration, technology of inserting a buffer using a Schmitt trigger into the conventional circuit has been largely studied, but the technology tends to cause a signal delay difference between different signal transmission paths.
Consequently, the conventional technology has a lot of problems from the point of view of a low power design and also the degree of integration.